Electronic devices, such as integrated circuits, are increasingly being used in different applications. One prevalent example of an application using integrated circuits is the computer. The central processing unit or units of most computers, including personal computers, is typically constructed from a plurality of integrated circuits.
During normal operation, many electronic devices generate significant amounts of heat. If this heat is not continuously removed, the electronic device may overheat, resulting in damage to the device and/or a reduction in operating performance. For example, the electronic device may encounter thermal runaway, with may damage the electronic device. In order to avoid such problems caused by overheating, cooling devices are often used in conjunction with electronic devices.
Over the years, the power of many electronic devices has increased along with the amount of heat generated by these devices. In addition, the size of electronic devices has generally decreased, resulting in greater amounts of heat being generated within smaller confines. In order to adequately cool these higher powered electronic devices without increasing their size, more efficient cooling devices and cooling devices with greater cooling capacities are required.
One such cooling device used in conjunction with electronic devices is a fan assisted heat sink. In such a device, a heat sink is formed from a material, such as aluminum, which readily conducts heat. The heat sink is usually placed on top of, and in physical contact with, the electronic device. The physical contact improves the thermal conductivity between the electronic device and the heat sink. Fasteners, such as screws, are often used to secure the heat sink to the electronic device, which maintains thermal conductivity between the electronic device and the heat sink. In addition, a thermally conductive compound is typically placed between the electronic device and the heat sink to enhance to heat transfer from the electronic device to the heat sink. This thermal conductivity results in heat generated by the electronic device being conducted into the heat sink and away from the electronic device. The heat in the heat sink is then dissipated into the surrounding atmosphere.
One method of increasing the cooling capacity of these heat sinks is by including a plurality of cooling fins that are physically connected to the heat sink. These fins serve to increase the surface area of the heat sink and, thus, maximize the transfer of heat from the heat sink to the surrounding atmosphere. In this manner, the heat sink draws heat away from the electronic device and transfers the heat into the surrounding air. An example of a heat sink is disclosed in U.S. Pat. No. 5,794,685 of Dean for HEAT SINK DEVICE HAVING RADIAL HEAT AND AIRFLOW PATHS and U.S. patent application Ser. No. 09/253877 of Hanzlik, et al. for COOLING APPARATUS FOR ELECTRONIC DEVICES, both of which are hereby incorporated by reference for all that is disclosed therein.
In order to further enhance the cooling capacity of a heat sink device, an electrically powered fan is often mounted within or on top of the heat sink. In operation, the fan forces air to move past the fins of the heat sink, thus, cooling the fins by enhancing the transfer of heat from the fins into the surrounding atmosphere. As the fins are cooled, heat can be drawn from the electronic device and into the heat sink at a faster rate. The fan typically draws air into the heat sink from the top of the heat sink, passes the air over the fins, and exhausts the air from the heat sink in the vicinity of the bottom of the heat sink. Accordingly, the exhaust air is hotter than the intake air. The operation and airflow of a heat sink device including a fan may, as an example, be described in U.S. Pat. No. 5,785,116 of Wagner for FAN ASSISTED HEAT SINK DEVICE, which is hereby incorporated by reference for all that is disclosed therein.
Two problems have been encountered with fan assisted heat sinks. The first problem is that the vibration of the fan coupled with the thermal expansions and contractions of the heat sink and the heat generating device break down the thermal conductivity between the heat sink and the heat generating device. Specifically, the heat sink and the electronic device expand and contract at different rates, which causes them to physically move relative to each other. The differing rate of expansion and contraction may cause a portion of the heat sink to separate from the electronic device causing the breakdown of the thermal conductivity between the heat sink and the electronic device. This breakdown results in the heat sink becoming much less efficient. Furthermore, this expansion and contraction may result in the thermal conductivity through the thermally conductive compound becoming disrupted, which further decreases the efficiency of the cooling device.
The second problem encountered with fan assisted heat sinks is due to air recirculating through the heat sink. In operation, cool air is drawn into the heat sink from the top of the heat sink across the top portion of the cooling fins. This air is then exhausted from the heat sink by directing the air across the bottom portion of the cooling fins. This circulation of air cools the entire heat sink. Under ideal conditions, the hot air exhausted from the heat sink is blown away from the heat sink and only cool air is drawn into the heat sink. Under many circumstances, however, the hot exhaust air disperses as it exits the heat sink. Some of this dispersed air then circulates up to the top of the heat sink rather than being blown away from the heat sink. This hot exhaust air is then drawn back into the heat sink by the force of the fan, which heats the air being drawn into the heat sink for cooling purposes. As this cycle repeats, this recirculating of exhaust air prevents efficient cooling of the heat sink because relatively hot air, not cool air, is being drawn across the fins.
Thus, it would be generally desirable to provide an apparatus and method which overcome these problems associated with cooling devices.